The present invention relates to a safety device for an elevator and, more particularly, to a safety device having inexpensive defective phase detecting means which can be applied to a control device using a microcomputer.
A control circuit for controlling the service supervision of an elevator ordinarily converts 3-phase A.C. power sources into a D.C. power source and uses the D.C. power source as a power supply. This is because the circuit employing the D.C. power source can easily constitute a sequence circuit by relays having highly reliable contacts by using as mechanical contacts necessary for an elevator, for example governor contacts and door contacts.
A power source for driving an A.C. motor for driving an elevator cage or a cage door employs 3-phase A.C. power sources.
If a 3-phase A.C. power source in a building develops a defective phase, the A.C. motors for driving the cage and the door become impossible to rotate forward or to reversely rotate, and an extremely dangerous state thus occurs. If the 3-phase A.C. power sources in a building develops a defective phase, it becomes impossible for the control circuit to function normally. Accordingly, if the 3-phase A.C. power source in the building develops a defective phase, in the prior-art elevator system, a safety device for abruptly stopping the elevator cage to secure the safety of passengers in the cage is employed.
FIG. 11 is a circuit diagram showing a prior-art safety device of an elevator. Reference numeral 1 denotes 3-phase A.C. power sources in a building, and numeral 2 denotes a converter for full-wave rectifying the 3-phase outputs of the 3-phase A.C. power sources 1 by using diodes. Numeral 5 denotes a defective phase detecting relay connected to the output terminals of the 3-phase A.C. power sources 1, numeral 6 denotes a safety relay of an elevator which outputs an abrupt stop command to an elevator cage and which is connected through a make contact G.sub.1 of a mechanical governor (not shown) and a make contact P.sub.1 of the defective phase detecting relay 5 between the output terminals of the converter 2. Numeral 7 denotes an up contactor which outputs an up command to a cage driving motor (not shown), and which is connected through a make contact UA.sub.1 of an upward command relay (not shown) and a make contact A.sub.1 of the safety relay 6 between the output terminals of the converter 2. Numeral 8 denotes a down contactor which outputs a down command to the cage driving motor and which is connected through a make contact DA.sub.1 of a downward command relay (not shown), and the make contact A.sub.1 of the safety relay 6 between the output terminals of the converter 2.
In the safety device for the elevator constructed as described above, when the output of the 3-phase A.C. power source 1 is normal, the defective phase detecting relay 5 is energized, and its contact P.sub.1 is accordingly closed. When the contact P.sub.1 is closed, a current flows in a circuit of the positive (+) terminal of the power source, the make contact P.sub.1 of the detective phase detecting relay 5, the make contact G.sub.1 of the mechanical governor, the safety relay 6 and the negative (-) terminal of the power source. Thus, the safety relay 6 is energized. When the safety relay 6 is energized, its contact A.sub.1 is closed. Therefore, the circuit of the positive terminal of the power source, the contact UA.sub.1, the up contactor 7 and the negative terminal of the power source is formed to energize the up contactor 7.
Here, if any one phase of the 3-phase A.C. power source becomes defective for any reason during the upward operation of the elevator cage, the defective phase detecting relay 5 is deenergized, and its contact P.sub.1 is opened. When the safety relay 6 is deenergized, its contact A.sub.1 is opened to deenergize the up contactor 7. Thus, since the power supply to the cage driving motor is interrupted, the upward operation of the cage is abruptly stopped. This similarly operates the cage even during the downward operation of the cage.
The above-mentioned defective phase detector is stipulated by the law to be installed as a safety device by the ANSI, CODE in the U.S.A. and by the CEN, CODE in Europe.
Since the prior-art safety device for the elevator is constructed as described above, an exclusive unit, such as the defective phase detecting relay must be employed. Thus, the elevator system becomes expensive. Further, in a controller for an elevator by a microcomputer, in order to load the output signal of a unit by the contact configuration of the defective phase detecting relay, it has such a drawback that an interface must be employed.